13,872 research outputs found
Governing equations of tissue modelling and remodelling: A unified generalised description of surface and bulk balance
Several biological tissues undergo changes in their geometry and in their
bulk material properties by modelling and remodelling processes. Modelling
synthesises tissue in some regions and removes tissue in others. Remodelling
overwrites old tissue material properties with newly formed, immature tissue
properties. As a result, tissues are made up of different "patches", i.e.,
adjacent tissue regions of different ages and different material properties,
within evolving boundaries. In this paper, generalised equations governing the
spatio-temporal evolution of such tissues are developed within the continuum
model. These equations take into account nonconservative, discontinuous surface
mass balance due to creation and destruction of material at moving interfaces,
and bulk balance due to tissue maturation. These equations make it possible to
model patchy tissue states and their evolution without explicitly maintaining a
record of when/where resorption and formation processes occurred. The time
evolution of spatially averaged tissue properties is derived systematically by
integration. These spatially-averaged equations cannot be written in closed
form as they retain traces that tissue destruction is localised at tissue
boundaries.
The formalism developed in this paper is applied to bone tissues, which
exhibit strong material heterogeneities due to their slow mineralisation and
remodelling processes. Evolution equations are proposed in particular for
osteocyte density and bone mineral density. Effective average equations for
bone mineral density (BMD) and tissue mineral density (TMD) are derived using a
mean-field approximation. The error made by this approximation when remodelling
patchy tissue is investigated. The specific time signatures of BMD or TMD
during remodelling events may provide a way to detect these events occurring at
lower, unseen spatial resolutions from microCT scans.Comment: 14 pages, 8 figures. V2: minor stylistic changes, more detailed
derivation of Eqs (30)-(31), additional comments on implication of BMD and
TMD signatures for microCT scan
Osteocytes as a record of bone formation dynamics: A mathematical model of osteocyte generation in bone matrix
The formation of new bone involves both the deposition of bone matrix, and
the formation of a network of cells embedded within the bone matrix, called
osteocytes. Osteocytes derive from bone-synthesising cells (osteoblasts) that
become buried in bone matrix during bone deposition. The generation of
osteocytes is a complex process that remains incompletely understood. Whilst
osteoblast burial determines the density of osteocytes, the expanding network
of osteocytes regulates in turn osteoblast activity and osteoblast burial. In
this paper, a spatiotemporal continuous model is proposed to investigate the
osteoblast-to-osteocyte transition. The aims of the model are (i) to link
dynamic properties of osteocyte generation with properties of the osteocyte
network imprinted in bone, and (ii) to investigate Marotti's hypothesis that
osteocytes prompt the burial of osteoblasts when they become covered with
sufficient bone matrix. Osteocyte density is assumed in the model to be
generated at the moving bone surface by a combination of osteoblast density,
matrix secretory rate, rate of entrapment, and curvature of the bone substrate,
but is found to be determined solely by the ratio of the instantaneous burial
rate and matrix secretory rate. Osteocyte density does not explicitly depend on
osteoblast density nor curvature. Osteocyte apoptosis is also included to
distinguish between the density of osteocyte lacuna and the density of live
osteocytes. Experimental measurements of osteocyte lacuna densities are used to
estimate the rate of burial of osteoblasts in bone matrix. These results
suggest that: (i) burial rate decreases during osteonal infilling, and (ii) the
control of osteoblast burial by osteocytes is likely to emanate as a collective
signal from a large group of osteocytes, rather than from the osteocytes
closest to the bone deposition front.Comment: 11 pages, 6 figures. V2: substantially augmented version. Addition of
Section 4 (osteocyte apoptosis
Lessons Learned from a 10-Year Collaboration Between Biomedical Engineering and Industrial Design Students in Capstone Design Projects
Engineers and industrial designers have different approaches to problem solving. Both place heavy emphasis on identification of customer needs, manufacturing methods, and prototyping. Industrial designers focus on aesthetics, ergonomics, ease of use, manufacturing methods, and the user’s experience. They tend to be more visual and more concerned with the interaction between users and products. Engineers focus on functionality, performance requirements, analytical modeling, and design verification and validation. They tend to be more analytical and more concerned with the design of internal components and product performance. Engineers and industrial designers often work together on project teams in industry. Collaboration between the two groups on senior capstone design projects can teach each to respect and value the unique contributions each brings to the project team, result in improved design solutions, and help prepare students for future collaboration in industry. Student feedback and lessons learned by faculty and students from a ten-year collaboration between engineering and industrial design students from Marquette University and the Milwaukee Institute of Art and Design, respectively, are presented. Students learned to communicate with people in other disciplines, appreciate the complementary skills of each discipline, and value different approaches to problem solving
Lessons Learned from a 10-Year Collaboration between Engineering and Industrial Design Students in Capstone Design Projects
Engineers and industrial designers have different approaches to problem solving. Both place heavy emphasis on identification of customer needs, manufacturing methods, and prototyping. Industrial designers focus on aesthetics, ergonomics, ease of use, and the user’s experience. They tend to be more visual and more concerned with the interaction between users and products. Engineers focus on functionality, performance requirements, analytical modeling, and design verification and validation. They tend to be more analytical and more concerned with the design of internal components and product performance. Engineers and industrial designers often work together on project teams in industry. Collaboration between the two groups on senior capstone design projects can teach each to respect and value the unique contributions each brings to the project team, result in improved design solutions, and help prepare students for future collaboration in industry. Student feedback and lessons learned by faculty and students from a ten-year collaboration between engineering and industrial design students from Marquette University and the Milwaukee Institute of Art and Design, respectively, are presented. Students learned to communicate with people in other disciplines, appreciate the complementary skills of each discipline, and value different approaches to problem solving
Osteoblasts infill irregular pores under curvature and porosity controls: A hypothesis-testing analysis of cell behaviours
The geometric control of bone tissue growth plays a significant role in bone
remodelling, age-related bone loss, and tissue engineering. However, how
exactly geometry influences the behaviour of bone-forming cells remains
elusive. Geometry modulates cell populations collectively through the evolving
space available to the cells, but it may also modulate the individual
behaviours of cells. To factor out the collective influence of geometry and
gain access to the geometric regulation of individual cell behaviours, we
develop a mathematical model of the infilling of cortical bone pores and use it
with available experimental data on cortical infilling rates. Testing different
possible modes of geometric controls of individual cell behaviours consistent
with the experimental data, we find that efficient smoothing of irregular pores
only occurs when cell secretory rate is controlled by porosity rather than
curvature. This porosity control suggests the convergence of a large scale of
intercellular signalling to single bone-forming cells, consistent with that
provided by the osteocyte network in response to mechanical stimulus. After
validating the mathematical model with the histological record of a real
cortical pore infilling, we explore the infilling of a population of randomly
generated initial pore shapes. We find that amongst all the geometric
regulations considered, the collective influence of curvature on cell crowding
is a dominant factor for how fast cortical bone pores infill, and we suggest
that the irregularity of cement lines thereby explains some of the variability
in double labelling data as well as the overall speed of osteon infilling.Comment: 14 pages, 11 figures, Appendi
Demand-driven and Cost Effective Production: What the Farmers Ought to know. A case of Local Chicken Enterprise in Masindi District-Uganda
Most African communities depend on agriculture for both income generation and food security and yet farming has faced and is still confronted with a lot of production and market related hardships. Despite all these constraints, farmers are stuck on agriculture as it’s the only definite way of earning a living. The mistake farmers and other agricultural practitioners continuously make is to produce first and look for the market later. This is where buyers and the middle men in particular exploit and a conclusion is eventually made by the producer that,” there is no money in agriculture.” Farmers including those who want to reap from agriculture need to first change their attitudes towards it and secondly produce what the markets are demanding at particular point in time. This therefore calls for institutionally guided farmer market research, enterprise selection, experimentation and enterprise development. Farmers can only benefit from agricultural production after carefully understanding what the buyer wants as in the type of the commodity, size, quantity, quality, frequency of supply, conditions of supply and the price the buyer is willing to offer among others. Where the selected enterprise has very high costs of production, the farmer should minimize costs buy substituting some inputs with local materials and also negotiate for a premium price and sign contracts with the buyers. Two farmer research groups in Masindi district in Uganda went through the above processes and have got success stories to tell.Agricultural and Food Policy, Consumer/Household Economics, Demand and Price Analysis, Farm Management, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, International Relations/Trade, Marketing, Productivity Analysis, Research and Development/Tech Change/Emerging Technologies,
Spontaneous parity breaking of graphene in the quantum Hall regime
We propose that the inversion symmetry of the graphene honeycomb lattice is
spontaneously broken via a magnetic field dependent Peierls distortion. This
leads to valley splitting of the Landau level but not of the other Landau
levels. Compared to quantum Hall valley ferromagnetism recently discussed in
the literature, lattice distortion provides an alternative explanation to all
the currently observed quantum Hall plateaus in graphene.Comment: 4 pages, to appear in Phys. Rev. Let
Thermodynamic and rheological properties of rhyolite and andesite melts
The heat capacities of a rhyolite and an andesite glass and liquid have been investigated from relative-enthalpy measurements made between 400 and 1800 K. For the glass phases, the experimental data agree with empirical models of calculation of the heat capacity. For the liquid phases, the agreement is less good owing to strong interactions between alkali metals and aluminum, which are not currently accounted for by empirical heat capacity models. The viscosity of both liquids has been measured from the glass transition to 1800 K. The temperature dependence of the viscosity is quantitatively related to the configurational heat capacity (determined calorimetrically) through the configurational entropy theory of relaxation processes. For both rhyolite and andesite melts, the heat capacity and viscosity do not differ markedly from those obtained by additive modeling from components with mineral compositions
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